Name changed for this post.
DSis (age 44) is vulnerable. She has various physical health conditions that restrict her mobility and her mental health over the years has been poor. She never got any meaningful qualifications and hasn't worked for probably two decades now. In her twenties she had some drug issues and also attempted suicide. She lives on benefits in a council flat. My parents live nearby. She's emotionally and practically very dependent on our mum. Our mum will take her out food shopping and to the pharmacy every week, for example. She doesn't drive and can't walk far (has a mobility scooter). She is single (never really had a proper relationship).
An "acquaintance" of a neighbour has recently "befriended" her. This man is allegedly a heroin addict and his partner has just died of an overdose. He is of no fixed abode and appears to survive by sofa surfing.
My sister is basically lonely and accepts this man's "friendship." He sleeps on her sofa and is at the flat a lot of the time, according to my mum. He has a set of keys.
Most concerning is that he also has physical possession of her mobile phone and bank cards. He persuaded her to get rid of her landline (although this was just for internet). Her remaining bills are all paid for by direct debit. According to my mum, he is buying their food using her money. I should add that she has a history of managing her money poorly. My parents help by managing her savings (with her consent; this is a small amount she received as inheritance from grandparents), as otherwise she would spend it all. She likes treating others and giving money away (in an attempt to buy friendship). She's recently gone overdrawn (allegedly due to the move to Universal Credit), meaning my parents cleared her overdraft from her savings.
My question is whether there is any crime in this man holding my sister's bank cards and mobile phone. It appears to be with her consent (she is refusing help / denying anything is wrong), but the relationship is clearly exploitative. I think the answer is no. I've nevertheless encouraged my mum to file a police report so there is a record of what is going on. I'm thinking that my sister could end up bankrupted, for example.
My mum is basically unable to contact my sister, as this man has her phone. My sister needs my mum for the weekly pharmacy trips for her medication, as she can't get there herself, and this man is not allowed to collect on her behalf as he is known by the pharmacy as a drug addict. So she is still making contact somehow (I think she is allowed her phone for this, and has once rung from a neighbour's.)
Am I right that there's no crime, and nothing we can do unless my sister wants help?